Membrane technologies such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are energy efficient and cost-effective ways for water purification and other liquid separations. NF membranes have been widely used for brackish water treatment, waste water reclamation, and water softening because they require relatively low operating pressure compared to RO. NF membranes also retain high water flux with good filtration efficiency toward small organic contaminants and multivalent ionic species, which cannot be easily removed by porous UF or MF membranes.
Referring to FIG. 1, a NF membrane 10 includes a support web 12, a porous midlayer 14, typically a polysulfone (PSF), and a barrier layer 16. This multilayer construction is referred to as a Thin Film Composite membrane (TFC). The barrier layer plays an important role in controlling separation performance, while the support layers provide sufficient mechanical strength so that the TFC composite membrane 10 can endure external operating pressure.